Secret communication employing signal sequence switching



P 1949- L. A. THOMPSON 2,482,039

SECRET COMMUNICATION EMPLOYING SIGNAL SEQUENCE SWITCHING Flled Sept. s,1945 2 Sheets-Sheet 1 I I I I 6? 56 I I I l I l I l I I I I .I I l I I II I l I I l I I I I I I I I I I l I I I I I I I I I I I I I I 85 I I I l---I I I l I l I I l. J L AD/O I 1 l 3,2 i I: AHE' B-PF fix; I I I IINVENTOR.

/ v (00/5 A. THOMPSON A TTOENEYS p 1949- L. A. THOMPSON 2,48 ,039

SECRET COMMUNICATION EMPLOYING SIGNAL SEQUENCE SWITCHING Filed Sept. 6,1945 2 Sheets-Sheet 2 B fig A r TOEA/EYS Patented Sept. 13, 1949 UNITEDSTAT SECRET COMMUNICATION EMPLOYING SIGNAL SEQUENCE SWITCHING Louis A.Thompson, Rocky River, Ohio, assignor to NEA Service, Inc., Cleveland,Ohio, 2. corporation of Delaware Application September 6, 1945, SerialNo. 614,772

6 Claims. 1

My invention relates to switching apparatus, particularly sequenceswitching for signal transmission.

It is an object of my invention to provide improved methods andapparatus for signal transposition and the security transmission ofinformation.

A further object of my invention is to avoid transients or effectsrecognizable as transitions or transfer points in the electricaltransmission of intelligence.

A further object is to provide electrical continuity between unrelatedsignal segments. Still another object of my invention is to transferelectrical signals back and forth between circuits with high precisionso as to avoid any overlap between signals and to avoid also any periodduring which no energy is present in the system.

Still another object of my invention is to control signal switchingphoto-electrically.

Further object of my invention is to control selection of channels forsignal transmission by selectively blocking various channels.

Other and further'objects, features and advantages of my invention willbecome apparent as the description proceeds.

In carrying out my invention in accordance with a preferred formthereof, I provide a punched tape in conjunction with a source of lightand a photo-electric tube for producing channel energization andblocking voltages in accordance with the pattern of slots punched in thetape, which is caused to travel at a uniform rate of speed preferablysynchronized with other apparatus. A plurality of circuits is providedeach controlled by a photo-electric tube associated with one of therowsof the slots in the moving tape. There may be a plurality of connectionsthrough which input signals are received where several signals are to betransposed among the various channels for security purposes. For thesake of simplicity however, the invention will be explained inconnection with an arrangement in which different signal elements orsegments of a single signal differing in time relation are transposed bymeans of the apparatus for the purpose of making the signalunintelligible to an unauthorized receiver. Preferably -in this casememory apparatus synchronized with the moving tape is employed for thepurpose of providing different segments of the same signal differing intime of occurrence.

Means are provided for causing signal output to be transmitted from oneof the circuits at a time and preferably means are provided forconverting the input signals into frequency variations to simplify theelemination of transition or transfer effects. The frequencymodulatedoutput signal is amplified and severely limited so that nopossible difference in signal level occurs at the transfer points wherethe circuit is switched from one channel to another. After limitation ofthe signal, it is filtered to reconvert the transposed signal wave toone having only sine wave components within the frequencymodulationfrequency range.

The output signal is transmitted by any suitable medium such as landwire, carrier, radio or the like. For reception of the signal suitableapparatus is provided for reversing the operations performed on thesignal prior to the transmission so as to rearrange the signal segmentsin the original order before application to an ordinary receiving devicesuch as a telephoto exposure head, telephone, telegraph or teletypereceiver or the like.

A better understanding of the invention will be afforded by thefollowing detailed description considered in conjunction with theaccompanying drawing in which Fig. 1 is a circuit diagram schematicallyillustrating an embodiment of my invention as used in the transmissionof transposed signals. Fig. 2 is a schematic diagram of receivingapparatus adapted for use with the apparatus of Fig. 1, and Fig. 3 is adiagram of a combined switching, signal coding, and memory apparatusutilizing a punched tape for control.

Referring to the drawings it is assumed that signals for transmissionare applied to an input terminal ll. Suitable means such as a memoryapparatus [2 are provided for recording and making available elements orsegments from the input signal differing in time relation. A pluralityof channels, in this case represented as three in number, are providedfor passing different signal elements. These three channels arerepresented by amplifiers 13, M, and i5 included in the respectivechannels. A signal sequence switching device It represented by theportion of the apparatus within the dotted lines is provided for controlof the sequence of signal elements supplied to the output circuit, whichincludes an amplifier ll to which the out puts of the amplifier l3, l4and [5 are connected in parallel.

Memory apparatus is arranged to provide three signal output circuits I8,19 and 2|. Preferably means are provided for converting the signals tofrequency modulated signals. For example three oscillators 22, 23 and 24may be provided, each having reactance-tube modulating means 25, 26

and 21, respectively, interposed between the circuits l8, I9 and 2| andthe oscillators 22, 23 and 24, respectively. For the sake of simplicitythe oscillators 22, 23 and 24 have been shown as separate units; butpreferably I employ a single fixed-frequency oscillator beating withthree variable frequency oscillators, each controlled by one of thesignal circuits l8, l9, and 2| and having a different average frequency.For example a frequency of 100 kilocycles may be chosen for thefixed-frequency oscillator, and; the. mid-range frequencies of thevariable oscillators may be 101, 102, and 103 kilocycles respectively.It will be understood, of course, that these specific numerical valuesare given merely by way of illustration and that the invention is notlimited to any specific values.

The signal switching device I6 includes a movable beam interceptor or ashutter means, a radiant beam source and a plurality of radiant energyresponsivedevices. The beam interceptor is illustratedas a moving tape 28, driven at a uniform rate ofspeed by a drum 2-9. The radiant beamsource most conveniently takes the form of a lamp 3|. The radiant-energyresponsive devices preferablytake the form of photoelectric tubes 32,33,and: 34. Means are provided for controlling-the transmission of signalsthrough the amplifiers 13-, I4 and I in response to thephotoelectric-tubes 32, 33 and 34. The tape 28 is provided with aplurality of rows of slots in this case three rows of slots 35, 36 and3'! corresponding in number to the number of photoelectric tubes and thenumber of transmission channels. Prefrably a beam-focusing arrangement,represented schematically by a single lens 38 and a slot 39 are providedin order to produce a thin ribbon oilight spread across the tape 28, ora plurality of beams aligned transversely across the tape 28, strikingthe respective slots 35, 5:18 and 37. For the sake of simplicity ofexplanation it is assumed thatjlig htfrom the lamp 3| has been brokeninto three separate beams 4!, 42, and- 49 adapted to be reflected bymirrors 44, 45 and 46, against the photoelectric tubes 32, 33 and 34,respectively. The complete paths of; all the light beams have beenshown, although with the tape 28 in the position illustrated, only thelight beam 4-2-is free 3 to pass through the associated'slot 41in thetape -28 and to strike the associated photo-electric oscillator 22 and ablocking tub 52. The amplifier I3 also has connections 53 tappingvoltage therefrom and supplying a pair of unilateral deviees such asfull wave rectifiers 54 and 55. Similar devices are associated with theamplifiers l4 and I5. The output connections 56, 5! and 58 qf theamplifiers are connected in parallel directly or indirectly to a commonoutput line 59 supplying the input to the amplifier IT,

The direct current-amplifier tube 48 has an anode or plate ,6connectedto a suitable source V ltager. epresen ted by the symbol Bjandhas a cathode 8-2 inseries with the primary winding 6312 an np t fq m 1t am l e L3, Alsoeonneeted in series with the winding 6. istbe s gnalick-un ube 4 av nsa cathod "65 connected to the cathode 86 of blockingtube 4 52. A cathode resistor 61 is connected between the cathode 65 ofthe blocking tube 52 and ground. The plate or anode 68 of the blockingtube 52, associated with the amplifier I3, is connected through aconductor 69 to output conductors H and '52 associated with therectifiers tapped into the other amplifiers. Thus the line H isconnected to a rectifier 13 having leads from the amplifier l4, and theline 12 is connected to the output terminal of the rectifier 14energized from the amplifier {-5, The blocking tube 15 associated withthe amplifier I4 is supplied with the direct current either from therectifier 55 associated with the amplifier +3 on the rectifier l9associated with the amplifier [5. In like manner each amplifier isprovided with a plurality of unilateral devices or rectifiers, each onesupplying direct current to the blocking tube of one of the otheramplifiers.

In order to eliminate the transient efiect of variations in amplitude oftransposed'wave segments and to suppress any indications of the pointsof transposition, a push pull limiterl'tis provided in -the output sideof the amplifier I! designed for severely limiting the wave. Forconverting the output of the limiter TI from-a rectangular wave or onehaving square tops, to

a wave containing only sine wave components of the frequenciesrepresented: by the output ofthe oscillators 22, 23- and 24-a-band-passfilter 18: is provided. Where the numerical values'of the frequenciesemployed are as previously assumed, so that the output-frequencies ofoscillators 22, 23 and 24 average- 1000,2900, and 3000 cycles,respectively, the filter 18 has band-passing frequencies lying in theregionbetween zero and 5000 cycles, for example. Preferablyan amplifier18 is provided for amplifying the output of the band-pass filter 18 andsupplying it to a suitable transmission channel, which may take the formof a wire or-carrier circuits, but for the sake of illustration isrepresented as a radio transmitter 8| including-radiator elements'82.

Preferably the tape 28 is so arranged as-to be coordinated withthe-memory apparatus L2 so-that the slot punching of the tape 28 maybeemployed also-for controlling the transposition arrangement and codingof the memory-device 12. Any suitable form of a memory apparatus may beemployed. The; arrangement illustrated comprises a travelling, magneticwire, tape or disc 84 having means for synchronizing itself with thepunched tape 28. This is indicated schematically in thedrawings-bymechanical connections consisting of the shaft 85, bevelgears 88 and8'l; and a shaft'88 connected to thesprocket drum 29drivingthe tape "28'. The mernorydevice I2 is provided with asignal-recording electr c-magnet 89, a plurality of signalpick-up.-electro-magnets "9|, 92-and 93 or -more (not shown) and anerasmagnetic record 84 by the recordingmflgnet 89,

before it is wiped oiT-or erased'by magnet 94. The erasingmagnet' 94-may be a permanentmagnet or a high-frequency electromagnet. The angularspaeine between the pick-up heads or electroma ne s 1 921.a may, e olate to th linsarg pac ns tween. h t ail ng e ds. of th successive slots95, 96' and 91" of the tape ZB' th at anode B8 of the blocking tube 52.

either thesame length of time is required for the magnetic disc 84 tomove through a unit spacing as for the tape 28, or the time ratio is anintegral number. For the sake of simplicity of explanation, a simplifiedpattern or arrangement of slots is shown but it is to be understood thatin practice a more complicated code may be and preferably is employed.The slots punched in the tape 28 may be of the same lengths or differentlengths and the spacing of successive slots may be difierent inaccordance with the code employed. It is unnecessary however to employgreat accuracy in the length of the slots, the determining factor is thespace from the trailing end of one slot to the trailing end of the next,for example, from the end 98 of the slot 96 to the'end 99 to the slot95. Preferably, as indicated, trailing ends of the slots overlap forreason which will be explained. The amount of overlapping and anyvariations therein have no effects on the accuracy and precision of theoperation of the signal transposition and sequence switching.

' Since the recording heads 9|, 92 and 93 of the memory apparatus I2 areoperated at different angular positions, a signal occurring during agiven time interval will be reproduced at successively later times bythe heads SI, 92 and 93. The arrangement of the tape 28 is such that theportions of a signal occurring during successive time intervals aredelivered to a channel separately as signal segments, and the signalsegments are rearranged and retransmitted out of their natural order.Thus when the light beam passes through only one of the slots in thecentral row such as slots 96 and 41, the photo-tube 33 is illuminatedcausing the amplifier I4 to operate. Similarly for the other amplifiersand the channels in which they are located. However, when light beamspass through two overlapping slots, one channel blocks the other so thatonly one channel is efiective.

When the tape 28 is in such a position that the light passes throughboth the slot 95 and the slot 96, the poto tubes 32 and 33 areilluminated. Current passes through tubes 32 and 33. Passage of currentthrough the photo tube 32, positively biases the D.-C. amplifier 48 torender it conducting. Voltage is applied from the terminal B through thetube 48 and the input transformer 63 to the anode 68 of the signal relaydevice or pickup tube 59 thereby energizing it. The latter is therebypre-set so as to permit a signal from beat frequency oscillator 22 toafi'ect the Pick-up tube 49 as soon as it becomes conducting. The signalpick-up tube I02 had previously been rendered conducting through theaction of light falling on the photo tube 33, so as to energize theamplifier I4 and supplypositive voltage to the Consequently the cathodeB5 of the pick-up tube 49 is positively biased by the flow of currentthrough the cathode resistor 61 of the tube 52. As soon as the tape 28moved to the point at which the edge 98 of the slot 96 cuts-off thelight beam 42, the tubes IIlI and I82, amplifier I4, the rectifier I3and the blocking tube 52 lose energization. At the same instant thepotential of the cathode 95 falls to zero and the tube 49 becomesresponsive to pass segments to the amplifier I3. Under thesecircumstances the amplifier I3 is first pre-set so that the signalpick-up tube 49 and the amplifier I3 'may pass current as soon ascurrent is cut-off from blocking tube52; In a similar manner theinterception of lights at the trailing edge of each slot very preciselyfixes the instant of signal transfer to the ne'x't'cliannel. In thepattern arrange ment of slots shown, in the drawing, for the sake ofillustration, light beams will pass successively through the slots 91,9B and assuming that the tape 28 is traveling downward. Consequentlysignal segments from the memory apparatus pickup heads SI, 92 and 93will be sent successively through the channels I3, I4 and I5 and appliedin this order to the common output line 59. However since the magneticrecording tape or disc 84 is traveling in a direction from the pick-uphead 9! to 93 the signal segments actually occurring last aretransmitted first so that confusion is introduced in the transmittedsignal. The speed of the operation is such that very short segments aretransposed and'consequently the signal emitted from the radiotransmitter 8| is not transcribable or decipherable. By suitablearrangements of the slots in the tape 28 other and more complicatedtranspositions are provided making it still more diflicult to decipherthe transmitted signal.

In order to receive and decode the signal it is necessary to havecorresponding apparatus employing a transposition controlling anddecoding tape corresponding exactly with the tape 28. A suitablereceiving apparatus may comprise a radio receiver III having antennaeII2 corresponding to the transmitter antennae 32, a preamplifier IIU, apush pull limiter II3 for removing the fading eiiect, preferably anadditional amplifier I It, memory apparatus I I5 corresponding to thetransmitter memory apparatus I I2, and signal switching apparatus H9,corresponding to the. transmitter signal switching apparatus .I9. Bylimiting the output to a predetermined value independent of inputstrength or fading, the limiter I I3 overcomes the effect of fading. Theprinciple of operation of limiters is described in Basic Radio, by Hoag,1942 edition, page 2'74, referring to Fig. 33C and in Ultra-HighFrequency Techniques, by Brainerd et al., 1942 edition, pages 179, 267and 283. The switching apparatus H6 is provided with three output linesH1, H8 and I I9 corresponding respectively to the output lines 58, 5'!and 58. Preferably the receiver includes limiters I2I, I22 and I23 inlines H1, H8 and H9, and also amplifiers I24. The output terminals ofthe amplifiers I24 are connected directly or indirectly in parallel to apair of conductors I25 to which a suitable device I28 is connected suchas a telephoto exposure head, a teletypewriter, a

telephone receiver including a detector or other reception device,depending upon the input signal to the transmitter. The memory apparatusH5 and the signal sequence switching apparatus IIIi are provided withdriving motor means I21 for operating the two devices H5 and IIG.Suitable means (not illustrated) are provided for causing the motor 83at the transmitter and the motor IZI at the receiver to operatesynchronously and exactly in phase. Such means may take the forms ofsynchronizing drives or synchronizing signals such as employed intelephoto and television circuits.

The signal switching apparatus I I9 is indicated in block form but ispreferably identical with the arrangements shown within the dotted lineIII of Fig. 1. It includes tape such as the tape 28 of Fig. 1 which isidentical there with same punching arrangement. In case the receivingapparatus indicated in Fig. 2 should be located in such a position thatit may fall in enemy hands during military use or there is danger thatunauthorized operators of the signal transmission circuits may obtainaccess thereto during cominercial use, the tape: of the receivingapparatus removed before leaving the receiving apparatus ungu'arded.Without the. proper tape.- serving as.:-.a key tov the transposition itis; not possible. for an'unauthorized personeverr-with similarreceiving. apparatus to obtain signalswhich convey intelligence. Even ifreceived signals should be recordedand should; be: examined by decodingexperts allowed a considerable. period of time, decoding Wouldbeimpossible because the points of transition are not detectable.Thesignal segments into which the original segment was cut fit together.without revealing transition points since only frequency changes areinvolved and opera-tesrvery precisely in starting the transmission of.signal segment over one channel at the instantof termination of thetransmission over another. channel. There are no transition; or decayefiectsbywhich a person attempting to decode the recorded signal canobserve the points of transition.

'I heonly way of decoding the signal segment in theoriginal order is toemploy a tape in the switching, apparatus i it at the receiver which isidentical with the tape 28' at the transmitter. Consequently the simpleoperation of removing such a tape renders it impossible for unauthorizedpersons to receive signals even though they may obtain access to-thereceiver. Thus the apparatus maysafely be employed for security purposeseven if those operating the receiver should find itFi-mpossibleto retaincontrol thereof and should noteven have. time to destroy the receiver.The tapemay; be composed of inflammable material or of metal, but evenif composed of metal it is readily destroyed: since thin metal would beemployed. Even though the light metal tape may not be consumedby fire itwill be destroyed by the heat. For example it'may also be destroyed bypassage of electrical current to heat it to glowing temperatures. Thiswill serve to damage it to such an extent that it will not operate andthat the slot coding is not reproducible.

Thin metal tape has the advantage of maintenance of accuracy of slotspacing independently of humidity conditions.

In order to simplify the precise synchronization of the moving elementsof the memory apparatus i2 andthe moving tape 28 f the signal sequencedevice it, a tuning fork drive or a moving light'interceptor may beemployed as the common moving element for both devices. For example aslotted'motion picture film having sound tracks at'the edge may beemployed for the operation of both the photo-electric cells 22, 23 and24 and forenergizing the memory device units photoelectrically.Preferably a steel tape is employed for the sake of accuracy. Asindicated in Figure 3, a tape {29 is employed composed of steel havingslots I28, I29 and lfii cut therein with slot spacing corresponding tothe spacing of the magnetic pick-up-head's SI, 92 and 93 arranged alongthe edge I32 of the tape lZ'i. It should be understood that therecording head 89 is arranged in advance of. the pick-up heads 9!, 92and. 93 and that an erasing magnet 94 may be provided as previouslydescribed.

While I have described my invention as embodied in concrete form and. asoperating in a s-peeificmanner in accordance with the provisions of thepatent statutes it should be understood that I donot limit my inventionthereto, since various modifications thereof will suggest themselves tothose skilled in the. art without departing from 8 the'spirit of myinvention,- the scope of which 'is set forth in the annexed claims.

I claim: 7

1. Signal sequence switching apparatus. comprising in combination a.plurality of transmis mison channels, a plurality of blockingdevices,each one adapted to block one of said. channels when. energized, meansproviding a plurality of lightbeams, a moving, tape arranged tointercept said light beams with each beam striking a different distancefrom the edge of the tape, said tape having. longitudinal rows of slots,each row of slots passing through one of said light beams, whereby saidlight beams are intermittently passed and-intercepted as the tape moves,said slots being arranged according to a fixed pattern and each slotlongitudinally overlapping a slot in. another row, a plurality ofphoto-electric responsive devices beyondsaid tape with respect to saidlight providing means, direct current amplifiers actuated by saidphoto-electric devices, and connections from each one of said amplifierstooneof said channels. for energizing the same, unilateral means betweeneach of said amplifiers and allof the blocking devices except the oneassociated with the channel energized by the same amplifier, uniiateralmeans being connected to said respective blocking devices for energizingthe same in response to amplifier output, memory apparatus for recordingthe input to each blocked channel and for subsequently transferring therecorded signals to said. channels.

2. A signal sequence switching apparatus. comprising in combination aplurality of transmission channels, a plurality of blocking devices,each one adapted to block one of said channels when energized, meansproviding a plurality of light. beams, moving tape arranged to interceptsaid light beams with each beam striking a differentdistance from theedge of the tape, said tape having longitudinal rows of slots, each rowof slots passing through one of said lightbeams whereby said light beamsare intermittently passed and intercepted as the. tape moves, said slotsbeing arranged according to a fixed pattern and each slot longitudinallyoverlapping a slot in another row, a plurality of. photo-electricresponsive devices beyond. said tape with respect to said lightproviding means, direct current amplifiers-connected to saidphoto-electric devices, connections from each of said amplifiers to oneof said channels for energizing the same, and simultaneously energizingeach of said blocking devices except the one associated with the channelenergized by said amplifier.

3. A signal sequence. ap aratus comprisingin combination a plurality oftransmission'channels, a plurality of blocking devices each one adaptedto. block one of said channels when energized, means'provi'ding aplurality of light beams, moving. shutter meansarranged to interceptsaid light beams with each beam striking a difierent distance from theedge or" the shutter means, said shutter means having rows of slots,each row passing through said light beam whereby said light beams areintermittently passed and inter.- cepted as the shutter means moves,said slots being arranged according to a predetermined pattern and eachslot longitudinally overlapping a slot in another row, a plurality oiphoto-electric responsive devices beyond said shutter means withrespect. to said light providing means, direct current amplifiersactuated by said photo-electric devices, and connections between said;channels and said direct current amplifiersforprecondi- 9 tioning eachchannel to be energized with corresponding light beams permitted to passthrough said shutter means and for energizing the blocking means of theother channels simultaneously therewith, whereby each channel becomesfinally energized when the channel is unblocked.

4. Signal sequence apparatus comprising in combination a signal source,a plurality of transmission channels, a plurality of blocking deviceseach one adapted to block said channel when energized, means providingradiant energy beams, moving shutter means arranged to intercept andpass such beams intermittently according to a predetermined pattern,each of said radiant energy beams corresponding to one of said channels,a signal relay device for each channel controlling transmission ofreceived signals through it, each of said signal relay devices being ofthe type effective to permit transmission through its channel only whenenergized, means responsive to passage of the radiant energy beamcorresponding to a given channel for simultaneously energizing thesignal relay device of the corresponding channel and energizing theblocking means for the other channels, whereby the interception of theradiant energy beam terminates the blocking of a given channel, releasessuch channel for signal transmission, and signals are transferred insequence from one channel to another according to the pattern of saidshutter means.

5. Signal sequence apparatus comprising in combination a plurality oftransmission channels, a plurality of blocking devices each associatedwith one of said channels, a source of radiant energy, a plurality ofradiant energy responsive devices, a moving radiant energy interceptorwith slots in rows each corresponding to one of said energy responsivedevices, and connections from each of said energy responsive devices forenergizing one of said channels and blocking the remainder, wherebysignals are .-passed through said channels in accordance with a codedetermined by its slot arrangement of the said moving interceptor.

6. The method of signal transmission which comprises recording of thesignal to be transmitted in segments occurring in difierent intervals oftime, transmitting signal segments through separate channels,transposing the sequence of transmission through said channels inaccordance with a predetermined code with transmission through only onechannel at a time, combining the transposed signal segments to form acontinuous unbroken transmission, limiting the output amplitude tosuppress decay effects at the instants of transfer, transmitting theoutput of the limiter, receiving such output and recording successivesignal segments, transposing the signal segments in accordance with thesame transposition code employed in the transmitter for restoring theoriginal signal sequence in difierent channels, limiting the output ineach channel and combining all the outputs for utilization in areceiving device.

LOUIS A. THOMPSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,048,081 Riggs July 21, 19362,094,132 Miller Sept, 28, 1937 2,282,046 Goldsmith May 5, 19422,300,664 Francis Nov. 3, 1942 2,364,210 Guanella Dec. 5, 1944 2,380,982Mitchell Aug. '7, 1945 2,401,888 Smith June 11, 1946 2,403,561 SmithJuly 9, 1946 2,406,353 Myers Aug. 27, 1946 Certificate of CorrectionPatent No. 2,482,039 September 13, 1949 LOUIS A. THOMPSON d that errorsappear in the pr ted specification of the above tube 59 It is herebyeertifie numbered patent requiring correction as follows:

Column 5, line 48, for terminal B read terminal 13+; line 51, for readtube 49; and that the said Letters Patent should be read with thesecorrecti m to the record of the case in $111.36 Patent Oflice.

the same may confer Signed and sealed this 17th day of January, A.

one therein that THOMAS F. MURPHY,

Assistant Commissioner of Patents.

flertificate of Qorrection September 13, 1949 Patent No. 2,482,039

LOUIS A. THOMPSON It is hereby certified that errors appear in theprinted specification of the above numbered patent requiring correctionas follows:

Column 5, line 48, for terminal B read terminal 13+; line 51, for tube59 read tube 4.9; and that the said Letters Patent should be read withthese corrections therein that the samemay conform to the record of thecase in the Patent Ofiice.

Signed and sealed this 17th day of January, A. D. 1950.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.

